1. Field of the Invention
The present invention relates to a shutter device including a first blade and a second blade, and to an image pickup apparatus.
2. Description of the Related Art
In general, as a shutter used in a single lens reflex camera, a focal-plane shutter including two sets of light-shielding members, first blades (a first curtain) and second blades (a second curtain), is used. Prior to exposure, the first blades of the focal-plane shutter cover an aperture. Then, when shooting is performed, first, the first blades withdraw from the aperture to start the exposure on an image pickup surface. Thereafter, after a predetermined time, the shutter device operates so that the second blades cover the aperture.
When a high-speed time control is performed at the focal-plane shutter, the width of a slit, formed by portions of the first blades and the second blades, is reduced to achieve the high-speed time control.
Japanese Patent Laid-Open No. 6-265975 discusses a focal-plane shutter including a detecting unit that makes use of a light-emitting diode and a photo-transistor to detect the width of a slit, formed by portions of first blades and second blades, that is, a shutter-blade open time. In addition, it discusses a shutter device that can detect whether or not a shutter precision is within a predetermined range.
In recent years, shutter speed is remarkably being increased, and the width of a slit, formed by portions of first blades and second blades, is being reduced. Therefore, as in the shutter device discussed in the aforementioned document, there is a problem that, when an open time of shutter blades is detected by a detecting unit that makes use of a light-emitting diode and a photo-transistor, a difference is produced between an actual slit open time and the slit open time detected by the detecting unit.
Such a related shutter is described with reference to FIGS. 4 to 9. FIG. 4 is a front view of a related focal-plane shutter, showing a state in which charging of shutter blades is completed. Reference numeral 1 denotes a shutter bottom plate having an aperture 1a at a central portion thereof. Reference numeral 21 denotes a first blade driving lever rotatably mounted to a shaft 1c of the shutter bottom plate 1 and rotationally biased clockwise in FIG. 4 by a torsion spring (not shown). The first blade driving lever 21 is provided with a blade driving pin 21a at the illustrated right end thereof, and is connected to a first main blade arm (described later). A first armature 22 is mounted to the illustrated top portion of the first blade driving lever 21. In the completed charging state shown in FIG. 4, the first armature 22 is in contact with an adhesion surface of a first blade electromagnet 23 affixed to a bottom plate (not shown).
Reference numeral 24 denotes a second blade driving lever rotatably mounted to a shaft id of the shutter bottom plate 1 and rotationally biased clockwise in FIG. 4 by a torsion spring (not shown). The second blade driving lever 24 is provided with a blade driving pin 24a at the illustrated right end thereof, and is connected to a second main blade arm (described later). A second blade armature 25 is mounted to the illustrated top portion of the second blade driving lever 24. In the completed charging state shown in FIG. 4, the second blade armature 25 is in contact with an adhesion surface of a second blade electromagnet 26 affixed to a bottom plate (not shown).
Reference numeral 27 denotes a charge lever, which is rotatably mounted to a shaft 1e of the shutter bottom plate 1. In the completed charging state shown in FIG. 4, cam surfaces 27a and 27b of the charge lever 27 maintain the first blade driving lever 21 and the second blade driving lever 24 in the shutter charge state shown in FIG. 4 through a charge pin 21b of the first blade driving lever 21 and a charge pin 24b of the second blade driving lever 24.
FIG. 5 is a front view of the completed charging state of the shutter blades, and FIG. 6 is a perspective rear view of the completed charging state of the shutter blades.
Reference numeral 2 denotes a first main blade arm, which is rotatably mounted to a shaft 3 mounted to the shutter bottom plate 1. Reference numeral 4 denotes a first sub blade arm, which is rotatably mounted to a shaft 5 mounted to the shutter bottom plate 1. Reference numeral 6 denotes a first blade unit (first curtain) constituting the shutter blades and including four blades, a first blade 6a, a second first blade 6b, a third first blade 6c, and a fourth first blade 6d. These first blades 6a to 6d are rotatably mounted to the first main blade arm 2 and the first sub blade arm 4 through shafts to constitute a link mechanism. Accordingly, when the first main blade arm 2 is rotated to the right in FIG. 5 by the first blade driving lever 21, the aperture 1a of the shutter bottom plate 1 opens as the first blade unit 6 is folded.
Reference numeral 7 denotes a second blade unit (second curtain) constituting, along with the shutter blade unit 6, the shutter blades, and having the same structure as the first blade unit 6 (that is, including four second blades, a first second blade to a fourth second blade). The second blades are connected to a second main blade arm 8 and a second sub blade arm 9 through shafts to constitute a link mechanism. Accordingly, when the second main blade arm 8 is rotated to the right in FIG. 5 by the second blade driving lever 24, the aperture 1a of the shutter bottom plate 1 is closed as the second blade unit 7 is opened from its folded state.
Reference numeral 10 denotes a photo-reflector (hereunder referred to as “PR element”) including a light-emitting diode (hereunder referred to as “LED”) and a photo-transistor (hereunder referred to as “PTR”). As shown in FIG. 6, the photo-reflector 10 is formed so that, during shutter operation, it measures an open time of the shutter blades on the basis of reflection of light, emitted from the LED, from a mirror 11 (shown in FIG. 7 and described later) through a hole 1b in the shutter plate 1.
FIG. 7 is a block diagram of an electrical structure of a camera including the above-described focal-plane shutter. Reference numeral 101 denotes a central processing unit (CPU) that controls the entire camera. Reference numeral 102 denotes EEPROM that stores, for example, camera function data. Reference numeral 103 denotes a main switch that starts the camera body. Reference numeral 104 denotes a first switch that is turned on when a release button (not shown) is pressed to a first stroke position, to start, for example, a photometric operation or a focal-point detecting operation. Reference numeral 105 denotes a second switch which turns on when the release button is pressed to a second stroke position, to start a release operation for exposure. Reference numeral 106 denotes a photometric sensor, and reference numeral 107 denotes a distance-measuring sensor using a publicly known CCD line sensor.
Reference numeral 108 denotes a lens controlling circuit that controls driving of a replaceable shooting lens 109 of a single lens reflex camera. Reference numeral 110 denotes a shutter controlling circuit connected to the first blade electromagnet 23 (which controls operation of the first blade unit 6 of the focal-plane shutter) and to the second blade electromagnet 26 (which controls operation of the second blade unit 7 of the focal-plane shutter). Reference numeral 10 denotes the aforementioned PR element including an LED 10a and a PTR 10b. The PR element is formed so that the CPU 101 controls light emission from the LED 10a, causes projection light of the LED 10a to be reflected by the mirror 11, and causes the reflected light to be receivable by the PTR 10b. In this structure, operation of a shutter blade that passes between the PR element 10 and the mirror 11 is detected. Reference numeral 111 denotes a motor, which, on the basis of a control signal from a motor controlling circuit 112, drives a mirror charge mechanism 113 and a shutter charge mechanism 114, drives a mirror (not shown) during a shooting operation, and controls driving of the charge lever 27 that charges the shutter.
Next, operations of portions, related to the operation of the focal-plane shutter, of the camera having the above-described structure will be described.
First, in a state in which the first blade electromagnet 23 and the second blade electromagnet 26 of the shutter are electrified, the mirror (not shown) is withdrawn from a shooting light path by the operation of the motor 111. At the same time, the charge lever 27 is rotated counterclockwise from the state shown in FIG. 4 by the operation of the motor 111, and the first blade driving lever 21 and the second blade driving lever 24 are made rotatable clockwise in FIG. 4 by biasing force of a driving lever spring (not shown). At this time, the first blade electromagnet 23 and the second blade electromagnet 26 are in an electrified state. Therefore, the first curtain armature 22 and the second curtain armature 25 are attracted to and held by the first blade electromagnet 23 and the second blade electromagnet 26, respectively, so that the first blade driving lever 21 and the second blade driving lever 24 are held in the state shown in FIG. 4. When, in this state, the electrification of the first blade electromagnet 23 is stopped, the first blade driving lever 21 rotates clockwise in FIG. 4 by the biasing force of the driving spring (not shown), so that the first main blade arm 2 (shown in FIG. 5) also rotates. By this, the first blade unit 6 starts to open.
Next, when the electrification of the second blade electromagnet 26 is stopped, the second blade driving lever 24 rotates clockwise in FIG. 4 by the biasing force of the driving spring (not shown), so that the second main blade arm 8 (shown in FIG. 5) also rotates. By this, the second blade unit 7 starts to close. The operation of the shutter is controlled as a result of controlling a timing in which the electrification of the first blade electromagnet 23 and that of the second blade electromagnet 26 are stopped.
During the operation of the shutter, the LED 10a of the PR element 10 is made to emit light, and the light reflected from the mirror 11 is received by the PTR 10b through the hole 1b of the shutter bottom plate 1. Accordingly, the open time of the shutter blades is measured.
FIG. 8 illustrates a change in output voltage of the PTR 10b during the operation of the shutter, with the horizontal axis representing time and the vertical axis representing the voltage of the PTR 10b. A waveform 31 during a time in which the shutter is fully opened is obtained, so that a result of measurement of a time T1 is obtained with a voltage determination level 32 as a reference.
FIG. 9 is a perspective rear view showing a state in which the shutter is operating at a maximum speed time ( 1/8000 seconds). To make it easier to see FIG. 9, the shutter bottom plate 1 is not shown. A high speed time of the focal-plane shutter is achieved by controlling the width of a slit S formed by the first blade unit 6 and the second blade unit 7. However, when the width of the slit S is reduced, as indicated by a waveform 33 shown in FIG. 8, the second blade unit 7 arrives before the first blade unit 6 passes completely in front of the PR element 10. Therefore, the voltage of the PTR 10b, which corresponds to the output voltage of the PR element 10, is not a voltage indicating “total bright state.” Rather, it is a voltage indicating “a dark state.”
Further, when the shutter precision is reduced due to a change in, for example, durability, and the width of the slit S is further reduced, as indicated by a waveform 34 shown in FIG. 8, the voltage of the PTR 10b, which corresponds to the output voltage of the PR element 10, does not reach the voltage determination level 32. Therefore, the shutter open time cannot be measured.
Even if, in the above-described condition, an attempt is made to correct the change in the shutter precision or to detect the closing of the blades, the correction of the change in the shutter precision and the detection of the closing of the blades cannot be performed precisely.